Again, wide lines are deprecated but not removed in the Core GL contexts. The GL ARB specifically mentions this in the GL 3.1 spec (Appendix G). Since the ARB went to the trouble of specifically singling out wide lines to be kept in the core profile, I somewhat doubt they'll be removed, especially since they seem to have stopped deprecating and removing features. You can use this on OSX and all other core GL implementations, unless you're adverse to using a deprecated feature.

That's a good point, you do have to check the GL_LINE_WIDTH_RANGE (or GL_SMOOTH_LINE_WIDTH_RANGE, if you are using smooth lines). Both AMD and Nvidia drivers on Linux and Windows support the same aliased line ranges in the core profile as they do in the compatibility (AMD: 1 63, Nvidia: 0.5, 10). Intel graphics has a range of 1,1 (no line widths other than 1 are supported). Apple isn't known for supporting deprecated features, so they apparently set it to 1,1 as well.